Method of making squirrel cage rotors



Aug. 9, 1938. G. A. WATERS 2,125,970

METHOD OF MAKING SQUIRREL CAGE ROTORS FiledJan. s, 1956 FIG.8. 9 F162. 8

FIG.6

F l G INVENTOR.

l A.WAT'ERS 33 g:

A TTORNEY.

Patented Aug. 9, 1938' PATENT OFFICE LIETHOD OF MAKING ROTOR SSQUIRRELCAGE Granville A. Waters, University City, Mo., as-

signor to Wagner Electric Corporation, St.

Louis, Mo., a

corporation of Delaware Application January 6, 1936, Serial No. 57,707

5 Claims.

My invention relates to squirrel cage rotors for dynamo-electricmachines. Such rotors are commonly made by casting the rotor bars andend rings into. and around the assembled laminae forming the core of therotor. Rotors thus manufactured have certain disadvantages. Theshrinkage of both the bars and rings subject the structure toundesirable strains. Further, blow-holes often occur in the bars andrings causing variations in their resistance with consequent variationsin torque for different rotor positions with respect to the statormember, which irregular torque action results in what is known asratchet action or saddle formation. Another serious difficultyexperienced with cast rotors is that during the casting period the metalof the bars oozes from the inside of the slots to the periphery of therotor between the laminae thus short circuiting the individual laminaand causing stray losses.

The object of the present invention is to overcome the difficultiesabove referred to by forming either the end rings alone or both the barsand end rings of powdered metal consolidated under pressure. This methodof forming the rotorhas the further advantage that by suitable selectionof material any desired ohmic resistance may be obtained in the rotor.

In the accompanying drawing, which illustrates a rotor made inaccordance with my invention and the method of making the same, Figure 1is a sectional view showing the method of assembling the laminae;Figure'2 is a sectional view showing the assembled laminae positioned ina mold; Figure 3 is an enlarged view of one end of the mold aftercompression of the powdered material; Figure 4 is a plan of one form oflaminae; Figure 5 is a plan'view of a portion of another form oflaminae; Figure 6 is a view showa modified form of bar; Figure 7 is adiagrammatic view of a skewed type rotor; Figure 8 is a side view of acompleted rotor; and Figure 9 is a view on a greatly enlarged scaleillustrative of the preferred form of metal powder employed.

The rotor laminae I are punched in the usual manner and provided withslots 2 adjacent to their peripheries and with central shaft openings 3.The laminae are assembled on a dummy shaft l with their slots 2 inalignment and firm 'l'y clamped between flanges 5 and 6 on the ends ofthe shaft. The flange 5 at one end of the shaft may be formed integralwith or permanently secured to the shaft, but the other flange 6 is maderemovable to permit the insertion and removal of the laminae and isforced against the latter to tightly compress them by a nut 1 engagingthe threaded end 8 of the shaft. Bars 9 are inserted in the slots withtheir ends projecting beyond the core. The assembly is positioned in amold l having a cylindrical bore of the proper size to snugly fit theperiphery of the core formed by the laminae I. Sliding between theflange and the mold at each end is an annular compressing member orplunger H. The spaces between the ends of the plungers and the core arefilled with powdered metal l2 and the plungers are forced toward eachother by suitable means to consolidate the powder into an end ring l2having a volume of, approximately one-third of the volume of the powder.I find that a pressure of twentyfive tons per square inch, more, orless, will accomplish the result. After compression of the powder toform the end rings, the rotor is removed from the mold and heated in areducing atmosphere to a temperature of about 700 C. and maintained atthis temperature for several hours, after which it is allowed to cool tonormal temperature. This baking and cooling process completes thesolidification of powder forming the end rings into a mass of aconsistency similar to virgin metal.

If it is desired to give the rotor the lowest resistance possible forgiven dimensions, the bars iii are formed of copper and the powder l2for forming the end rings is also copper. If a higher resistance isrequired, either the bars or the rings or both may be made of brass. Itis also possible to use a mixture of different metal powders to form therings. For example, a mixture of nickel and copper may be employed toform end rings of relatively high resistance. A mixture of metal andnon-metal powders may be used to obtain extremely high resistance. Theform of powder which I prefer to employ in carrying out my invention isobtained by electrolytic means, and when highly magnified presents anappearance somewhat as shown in Figure 9, each particle of the powdershowing finger like protuberances on its surface. These protuberancesinterlock with those on adjacent particles under the extremely highpressure applied to the powder during the process of consolidating it.

If it is desired to form a rotor in which the slots are of thesemi-closed type, laminae I having slots I3 of the form shown in Figureare used. In this case it is desirable to provide means for preventingthe powdered metal from entering the mouths M of the slots. This is mostconveniently accomplished by placing at each end of the core one or morelaminal having closed slots, as is shown in Figure 3.

' When the rotor is o! the skewed type, that is, when the bars are notparallel with the axis of the core but are spirally disposed around it,the projecting ends of the bars are preferably bent so as to positionthem perpendicular to the ends of the core, as diagrammatically shown inFigure '7. The pressure used to consolidate the powder is thus appliedin a direction parallel with the projecting ends or the bars rather thanin a direction more or less transverse to said ends.

Instead of forming a ring of powdered metal at each end the rotor onlyone such ring may be employed, the bars being connected at the oppositeend in some other manner. One method of accomplishing this result is bythe use of "hairpin bars 15 such as shown in Figure 6. These bars areall inserted in the rotor slots from the same end, the bars beingconnected at the opposite end by a metal powder ring as above described.One end oi. the resultant rotor will have the appearance of a standardD. C. armature.

' While in my preferred construction the end rings of powdered metal areapplied to a rotor provided with bars formed of strips or rods oi. metalinserted in the slots of the core as shown,

both the bars and end rings may be formed from powdered metal. In thiscase it is advisable to' use a separate plunger for each core slot inorder to secure sufficient pressure to form solid bars from the powder.

Having fully described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

1. The method of forming a secondary member oil a dynamoelectric machinewhich comprises assembling slotted laminae to form a magnetic core,inserting metal bars in the core slots, said bars projecting from oneend or the core, applying metal powder to said end of the core andaround the projecting bars, and consolidating the powder under pressureto form an end 2. The method of forming a secondary member of adynamoelectric machine which comprises assembling slotted laminae toform a magnetic core, inserting metal bars in the core slots, said barsprojecting from one end oi. the core, applying metal powder to said endof the core and around the projecting bars, consolidating the powderunder pressure to form an and ring, and subjecting the resultantsecondary member to high temperature.

3. The method of forming a secondary mem' ber 01 a dynamoelectricmachine which comprises assembling slotted laminae to form a magneticcore, inserting metal bars in the core slots, said bars projecting fromone end of the core, applying to said end of the core and around theprojecting bars a metal powder, the particles oi which haveprotuberances on their surfaces, and consolidating the powder underpressure to form an and ring.

4. The method of forming a secondary member of a dynamoelectric machinewhich comprises assembling slotted laminae to form a magnetic core,inserting metal bars in the core slots, said bars projecting from oneend of the core, applying to said end of the core and around theprojecting bars a metal powder, the particles of which haveprotuberances on their surfaces, consolidating the powder under pressureto form an end ring, and subjecting the resultant secondary member tohigh temperature.

5. The method of forming a secondary member of a dynamo-electric machinewhich comprises assembling slotted laminae to form a mag netic core,inserting metal bars in the core slots, said bars projecting from oneend of the core, applying to said ends metal powder obtained byelectrolytic means, whereby the particles or said powder are providedwith surface protuberances adapted to interlock with each other,consolidating said powder under a pressure approximately twenty-fivetons per square inch to compress it to approximately one-third of itsoriginal bulk, and sintering the compressed powder at a temperature orapproximately 700 C.

GRANVHLE A. WATERS.

